前向引用

函數定義 在 函數調用 以前

而函數定義的順序可有可無

就如同變量的定義通常

a = 1
b = 2

#二者沒什麼不一樣

b = 2
a = 1

　　例

def bbb():
    print('this is b')
    aaa()
def aaa():
    print('this is a')
bbb()
#--------->
this is b
this is a

　　

def aaa():
    print('this is a')
def bbb():
    print('this is b')
    aaa()
bbb()
#----------->
this is b
this is a

　　不能夠這樣

def bbb():
    print('this is b')
    aaa()
bbb()
def aaa():
    print('this is a')
#--------->
Traceback (most recent call last):
this is b
  File "E:/pycharm/TEST.py", line 600, in <module>
    bbb()
  File "E:/pycharm/TEST.py", line 599, in bbb
    aaa()
NameError: name 'aaa' is not defined